Method of and apparatus for burning particle-form fuel



A. J. GRAM, JRj, ETAL 2,891,493

METHOD `oF ANU APPARATUS FUR BURNING PARTIULR-FORM FUEL June 23, 1959 ZYSheets-Sheet 1 Filed Sept. 7. 1954 .aL/u,... ATTORNEY June 23, 1959 A. J. GRAM, JR., ETAL 2,891,493

METHOD 0F AND APPARATUS FOR BURNING PARTICLE-FORM FUEL Filed sept. 7, 1954 2 sheets-sheet 2 INI/NTORS Jrzfzzr J Granglf BY MMM? Sy ATTORNEY United States APatent G 2,891,493 METHOD om j,sirianaLaV` "TUS Fon BUR- N1N` G PARTICLE-FORMf FUEL ArthurfJtGram, Jrg-Limavillafand-Warnie Lfsage, Louisville,Qhiorassignorsrto-The Babcockl & Wilcox Compuy,. New York, N.Y.,-a corporation of New- Jersey implication september "if,v 19521;. seria'lzNo.- r45m-358i 8 Claims. (Cl.- 1102l8)" j The present invention. relatesto amet'hod of. and apparatus: for. burning. afparticle-form. combustible solidmaferial;whichisfcharacterizedvr by. a. relatively low content ofashwhich is fusible under. normal.- combustion conditions. More. particularly,..the invention relates. tothe ofparticle-form solid materials. having both low combustible volatile and low ash. contents..

` Certain solid combustible materials occurring in. nature or. `formed during manufacturing vprocesses are characterized by low ash contents or when higher. percentages of ash are Apresent the ash is, at least partially, not fusible under ordinary furnace operating conditions. Frequentl'y,fsuch materials also have a low combustible volatile content anda hardness makingthem di'icult to .pulverize. Examples of solid combustible materials 4havinghigh lfilsioiry ltemperature ash may be found in certain-.wooda coal'sfwhei'ethe material may have either a-high or lwwvelatile content' and may ormay not be easy. to grind', Sblidmat'erials having both alow ash and' a low volatile bontet `are exemplified bythe coke residues'obtainedf in the -t'r'eatm'ent of petroleum,` more specifically,'fthe residues khown generally as lpetroleumwor pi'tc lcoke, in which the ash content is of the order of 110%' by weight of the coke and the volatile content is from. 1.0' to 7,0% by' weight. Such coke residues are usually extremely 'diicult to pulverize.

Attempts have been made to burn such low ash fuels iii heat absorbing equipment, such` as steamy boilers, to i"e`c:o'\`fer their high heat values. Usually, the fuels in their available form are too coarse and ltoo low in volatiles Yfor burning in suspension without pulverization, which is necessarily expensive due to their low grindability.V The fuels in their available form are, however, normally too ne for burning Von a travelinggrate because 'of excessive carry over of unburned material with resultcarbon loss and erosion of metal parts of the heat recovery equipment. l Y

In accordance with the invention, particle-form solid lmaterials of the character described can be successfully burned-ina high temperature cyclonic type furnace charnbei, the walls of Whichare maintained with a layer of Aviscous sticky refractory material thereon andonto which the coarser fuel particles are deposited by centrifugal `force and burn in situ', while the finer fuel particles are burned in suspension. When the fuel is low in combustible volatile content, auxiliary fuel is supplied in sufficient quantity to insure maintenance of furnace temperatures -abovethe ignition temperature of the coke and above the infusion-temperature of the furnace Wall coating material. Thewall coating material is formed-y by utilizing as the 'auxiliary vfuel either a particle-form high volatile bitu- -iiiin'ous coal having a relatively low'ash fusion tempera- 'ture l(eg. 200G-2400" F.) and at least a medium ash content, or fuel oil or gas in conjunction with an intermittent or continuous supply of'a refractory slag-forming .material having a fusion temperature below the normal mean furnace chamber temperature. In the latter case `and also Where the amount of coal ash available is insu- Nice 2. cient to supply the required amountlv of wall coating material, the molten slag-dischargedfromA the cyclone. furnace is. reduced" to a relatively finely divided4 or granulated condition by quenching; in water or by. rapid cooling, and recycled to the cyclone furnace chamber.

The various features of novelty#which-characterize the invention are pointed out with particularity` in theclaims annexed `to-and formingapart *ofA thisspecification. `For..

a better understanding'of the invention, its operating.v advantages and specific objects attained. by itsY use, reference. shouldbehad to the accompanying. drawings-and descriptive matter, in which a preferred. embodiment of the invention has-,been illustrated and described.

'Of the drawings:

Figi is a part-ly diagrammaticelevation.of an installation.incorporatingthe. present inventionand Fig.v 2 isY a. vertical sectionv taken. on. the. line: 212 of Fig.A 1.

In the drawings,.the.- invention is illustrated asv applied to. the.V combustion of av particle-form petroleum. coke which is theresidue of apetroleumrening process-of` the fluidizedbed, type, where the residuev is known as fuidized cokefhaving. a heat value. of. approximately 14,400. B.t'.u. per lb., a Hardgrove grindability index. value. of about l2,.and approximately 1% ash, 7 to. 10%1 sulphur, 4% combustible volatiles, and av neness of 10.0% through a 30`mesh U.S.v standardscreen. Enormous quantities. off such material are produced daily in: such processes, creating a diicult: disposal problem. In view of the Viineness of the coke, transporta-tionother thanin closed vehicles is impracticable.

As shown, the coke is burned in a cyclone furnace l0 of the general type disclosed in ULS. Patent No. 2,351,301. The cyclone combustion chamber or furnace comprises a cyclindrically shapedy shell or. barrel4 11 o'f circular cross-section and arranged with its axis sub,- stantially horizontal. The barrel 1I of the furnace 10 islined by refractory covered studdedl fluid cooledV tubes 12' arranged side-by-sid'e in opposite generally semi-circular loops having their ends opening to a. lower fluidinlet header ll?, and one of a pair of upper outlet headers 14, and 14. The headers 13, V14 and 14' have their axes substantially parallel to the axis of the cyclone furnace. The outer orV front end of the cyclone is formed. by a frusto-conical end portion 15 formed by similar refrac- 'tory covered fluid cooled tubes, and a central cylindrical inlet casing 16 concentric with the cyclone barrel. The opposite' end of the furnace is provided with tube and refractory construction forming, an outwardly flaring frus- 't'o-conical throat l? which, with the barrel 11, defines an annular pocket 18 surrounding a gas outlet or throat passage 20. The tubes forming. the Wall i7 are extended to form any upright wall of a primary furnace Z1 which, with a radiation chamber 22 separated therefrom by an inclined kbaffle 19, forms the lower portion of a steam generating and superheating unit of suitable, type. The lower part of the pocket 18 is provided with a slag discharge port 23 opening into the primary furnace 2l, so that any 'molten slag accumulating in the bottom of the furnace T10 will discharge across the floor 24, through a slagy hole Z5 therein, and thence into a slag tank 26.

As shown in Fig. l, an oil burner nozzle 27 is inserted into the inlet casing lo, with the axis ofthe burner coinciding with the axis of the furnace 10. The burner `nozrzle 27 is constructed and arranged to project jets of 'oil toward the circumferential wall of the furnacel'. The Vinlet section lo is provided with a tangential or Vinvolute connection to a fluid inlet duct 28 for the Virr- `tr'oduction of primary air and entrained solids, asherein- 'after-described, and in addition with an inlet connection `toa duct 30 for the controlled admission of tertiary combustion air to the furnace.

The barrel 11 of the furnace is formed with a horizontally elongated secondary air inlet section 31 for the tangential admission of a major portion of the combus tion air along the length of the furnace. As shown 1n Fig. 2, the secondary air inlet section is provided with a damper 32 pivoted so that the tangentially entering air is directed along the circumferential wall of the furnace near the top thereof. The velocity of the entering secondary air may be controlled as desired, with changes in the volume of air delivered.

In accordance with the invention, a plurality of circumferentially elongated inlet ports 33 are positioned in a row disposed longitudinally of the furnace at a position closely spaced circumferentially of the secondary air inlet section 31. As hereinafter described, the ports 33 are each supplied with a high velocity stream of airborne particle-form coke which is admitted tangentially, whereby the coke particles mix with the secondary air stream in an impinging relationship thereto to form a swirling mixture of coke and secondary air. With the described introduction of air and coke, the mixture tends to swirl around the inner circumference of the furnace in a generally helical path towards the gas outlet 20. The throat 17 causes the gases to reverse direction and move inwardly of the furnace before the gases leave the furnace with an advantageous tendency to separate entrained solid matter from the gases before passing to the primary furnace chamber 21.

Referring to Fig. l, the petroleum coke, which, as discharged from a uidized coke process, is of minus mesh fineness, is withdrawn from a coke storage bin 34 by a belt or pan type feeder 35 and regularly discharged through a rotating cup feeding and pressure sealing device 36. Conveniently, the feeder 35 is enclosed in an air-tight housing 37, with the rotary seal device 36 preventing ow of air or gases from the high pressure furnace 10 into the coke storage bin 34. From the rotary seal device, the coke discharges through a spout 38 into a transport pipe 4i) where the coke is entrained in a suitable carrier medium, such as air, for delivery to the cyclone furnace 10.

The coke and carrier air is discharged through the transport pipe 40 `and a flaring distributor 41 into a cylindrical manifold 42. The manifold receives the coke tangentially and discharges the coke through individual pipes 43, each connected with a corresponding port 33. The manifold 42 has a row of observation ports 44 in its side opposite the discharge pipes 43, the ports being closed by a removable cap member 45 having an observation window therein.

While low volatile low ash particle-form coke can be burned in a cyclone furnace of the character described with a supplementary fuel, such as oil or gas, it is advantageous to supply the cyclone with a material capable, with the furnace temperatures maintained, of forming a viscous sticky surface of molten material on the walls of the cyclone. Such a sticky surface will entrap the coarser particles of coke and retain them in the furnace in intimate scrubbing contact with the whirling stream of combustion air for a length of time suflicient to complete the combustion of the fuel. In the illustrated example of the invention, the petroleum coke has a lowash content which is insufcient to form an adequate sticky surface of molten material on the wall of the cyclone. In accordance with the invention, a suitable slag-forming solid material which is molten under the high temperature conditions maintained in the furnace is supplied to the furnace for this purpose. This material may take the form of various low temperature clays and sand, or lime or other non-combustible refractory materials, having melting temperatures in the range of 2000 to 2400 F. Alternately, the slag-forming material may be a finely divided high volatile bituminous coal of average ash content supplied with primary combustion 4 air through the pipe 28 and inlet section 16. Under the latter condition, the supplementary fuel, such as oll, delivered by the burner 27 to develop and maintain coke ignition temperatures in the furnace 10 may or may not be used, depending upon the amount of bituminous coal supplied.

When a non-combustible refractory slag-forming material of the type indicated is supplied to the cyclone furnace separately from or as embodied in the auxiliary fuel, it is `advantageous to recycle the slag-forming material for reuse in the furnace, so that the amount of make-up or fresh material will be kept to a For this purpose, the molten slag discharging through the slag hole 25 is arranged to fall into a pool 0f Water 46, maintained in the tank 26, which causes the slag to be quenched and shattered into granular solid form. The granular slag is continuously or intermittently removed from the slag tank by a screw conveyor 47 and discharged into a pneumatic conveyor 48 for delivery to a slag stofage hopper 50. The slag storage hopper is positioned above the cyclone 10 and is provided with a slag feeder 51 of the endless belt or apron type for the controlled discharge of the recycled slag through a rotary seal device 52 and a connecting spout 53 into the primary air duct 28 leading to the cylindrical inlet section 16 of the cyclone furnace.

In burning a low ash low volatile coke in the apparatus described, the combustion chamber is preferably brought up to the desired temperature by the combustion of oil fuel alone, and the non-combustible slag-forming material is added to the furnace to first form a viscous sticky lm of slag on the refractory-covered walls of the furnace 10. The slagging material discharging from the spout 52 is entrained by the stream of air passing through the duct 28 and with the tangential delivery of the mixture of air entrained solids, the solids are centrifugally distributed to the walls of the combustion chamber. The air necessary for the combustion of the oil fuel can be supplied through the ducts 28 and 30, supplemented, as required, by air delivered through the inlet 31.

With a combustion chamber temperature sufficient to ignite the coke and to maintain the sticky slag surface on the walls of the furnace, the coke is delivered through the ports 33 to the furnace 10. With the combustion of coke, the quantity of oil delivered to the burner 27 may be gradually reduced until normal operating conditions are established, with a heat input ratio of oil to coke, for example, of l to 4. The burning swirling mass of coke, air and combustion products moves in a helical ow path towards the outlet 20. Any excess slag-forming material drains to the chamber bottom and discharges through the port 23 and slag hole 2S into the tank 26. Substantially all of the slag-forming material delivered to the furnace 10 is recovered in the slag tank 26 and can be recycled through the system. Make-up material is added to the bin 59 as required.

While the illustrated embodiment of the invention discloses the use of oil as a source of high volatile fuel, it will be understood a gaseous fuel can likewise be used to accomplish the desirable results of the present invention. When a gaseous fuel is used, the fuel is preferably introduced through burners positioned in the secondary air inlet 31 for mixing the combustion air within the combustion chamber 10. It will be also understood that a medium ash high volatile bituminous coal may be used to provide both a high volatile fuel source for burning the low volatile coke, and as a source of slag-forming material for the sticky surface of the combustion chamber.

While in accordance with the provisions of the statutes we have illustrated and described herein a preferred embodiment of the invention, those skilled in the art will understand that changes may be made in the method of operation and form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of the invention may si'e'of'tlif feares,

Wlaf 'is'"cli'riied'is' 1. The method of burning a low-ash' :`o"1it'ei;t 'pi'clel form fuelat high ratesof zheat rel-ease lwhich comprises continuously introducing a stream of combustion air at a high velocity substantially:tangentially tothe circumferen- "tl wall of `a combustion chamber of circulai- ``os`s fsectioi continuously introducing th'exlprticlefr'i Tfuel into said combustion --chambenjcausing the air and fuel so introduced -to move aially lofthe combustion chamber though ahlicalpatir'alongfthe cic'lir'rferent'ialijwall of the"coinbusl'tionchamber, andi'rtroduig a slag-forming particle-form solid material of low combustible content relative to said fuel from a separate source to said chamber` while maintaining a combustion chamber temperature above the fusion temperature of said slag-forming solid material to form a viscous sticky surface on the circumferential wall of said combustion chamber in sufficient quantity whereby particles of said fuel tend to adhere to said sticky slag surface and to be Iburned by being scrubbed by the contacting combustion air.

2. The method of burning a low-ash content particleform fuel at high rates of heat release which comprises continuously introducing a stream of combustion ah at a. high velocity substantially tangentially to the circumferential wall of a combustion chamber of circular crosssection, continuously introducing the particle-form fuel into said combustion chamber, causing the air and fuel so introduced to move axially of the combustion chamber through a helical path along the circumferential wall of the combustion chamber, introducing a separate slagforming particle-form solid material to said chamber while maintaining a combustion chamber temperature above the fusion temperature of said slag-forming solid material to form a viscous sticky surface on the circumferential wall of said combustion chamber, whereby particles of said fuel tend to adhere to said sticky slag surface and to be burned by being scrubbed by the contacting combustion air, withdrawing the slag from said combustion chamber in a molten condition, quenching said molten slag to form particle-form solids, and recycling said kparticle-form solids to said combustion chamber.

3. The method of burning a low-ash and low-volatile content particle-form fuel at high rates of heat release which comprises continuously introducing a stream of combustion air at a high velocity substantially tangentially to the circumferential wall of a combustion chamber of circular cross-section, continuously introducing the particle-form fuel into said combustion chamber, causing the air and fuel so introduced to move axially of the combustion chamber through a helical path along the circumferential wall of the combustion chamber toward a gas discharge end thereof, introducing a slag-forming substantially non-combustible particle-form solid material from a separate source to the end of said chamber opposite to said gas discharge end, and separately introducing a high volatile fuel to said combustion chamber to maintain a combustion chamber temperature above the fusion temperature of said slag-forming substantially non-combustible solid material to form a viscous sticky surface on the circumferential wall of said combustion chamber, whereby particles of said fuel tend to adhere to said sticky slag surface and to be burned by being scrubbed by the contacting combustion air.

4. The method of burning a low-ash and low-volatile content particle-form fuel at high rates of heat release which comprises continuously introducing a stream of combustion air at a high velocity substantially tangentially to the circumferential wall of a combustion chamber of circular cross-section, continuously introducing the particle-form fuel into said combustion chamber, causing the air and fuel so introduced to move axially of the combustion chamber through a helical path along the circumferential wall of the combustion chamber toward 'and recycling -s'aia quent-.hed nag .to 'said earhbuisnofl "5'. The'ir'ne'tliodo'f bfning'a low-Lash and low-volatile content particle-form fuel at high rates of heat release which comprises continuously introducing a stream of combustion air at a high velocity substantially tangentially -to the circumferential wall of a combustion chamber of circular cross-section, continuously introducing the particle-form fuel into said combustion chamber, causing the air and fuel so introduced to move axially of the combustion chamber through a helical path along the circumferential wall of the combustion chamber, and introducing a minor quantity of a separate air-borne high volatile and ash containing particle-form solid Ifuel separately to said chamber to maintain a combustion chamber temperature above the ignition temperature of said 10W-volatile particle-form solid fuel and above the fusion temperature of the ash of said separate high volatile fuel to form a viscous sticky surface on the circumferential wail of Isaid combustion chamber, whereby combustible particles of both of said fuels tend to adhere to said sticky slag surface and to be burned by being scrubbed by the contacting combustion air.

6. The method of burning a low-ash and low-volatile content particle-form fuel at high rates of heat release which comprises continuously introducing a stream of combustion air at a high velocity substantially tangentially to the circumferential wall of a combustion chamber of circular cross-section, continuously introducing the particle-form fuel into said combustion chamber, causing the air and fuel so introduced to move axially of the combustion chamber through a helical path along the circumferential Wall of the combustion chamber, introducing a separate air-borne high volatile ash containing particle-form solid fuel to said chamber to maintain a combustion chamber temperature above the ignition temperature of said low volatile particle form solid fuel and above the fusion temperature of said slag-forming solid material to form a viscous sticky surface on the circum- 'ferential wall of said combustion chamber, whereby particles of said fuels tend to adhere to said sticky slag surface and to be burned by being scrubbed by the contacting combustion air, withdrawing the slag in molten form from said combustion chamber, quenching said molten slag, and recycling at least a portion of said quenched slag to said combustion chamber with said air-borne high volatile ash containing solid fuel.

7. Apparatus for burning a low-ash content particleform fuel at high rates of heat release comprising a combustion chamber of substantially circular cross-section dened by walls having an inner exposed refractory surface, a wall at one end of said combustion chamber including an inwardly projecting throat forming a gas outlet surrounded by an annular pocket, means for introducing a major portion of the air required for combustion in a stream tangentially to said circumferential wall, means for introducing said low-ash particle-form fuel into said chamber, means for introducing a separate Islag forming solid material into said combustion chamber to form a viscous sticky sunface lon the circumferential wall of said chamber, means for granulating said slag by quenching, and means for recycling said granulated slag-forming material to said combustion chamber.

8. Apparatus for burning a low-ash and low-volatile content particle-form fuel comprising a combustion chamber of substantially circular cross-section defined by Walls having an inner exposed refractory surface, a wall at one end of said combustion chamber including an inwardly projecting throat forming a gas outlet from said chamber surrounded by an annular pocket, means for introducing a major portion of the air required for combustion in a stream tangentially to `said circumferential Wall, `means for introducing said low-ash particle-form fuel into said chamber, means for introducing a separate high Volatile and slag-forming solid fuel into said combustion chamber to form a viscous sticky surface on the circumferential Wall of said furnace, means for collecting said slag in molten form in and removing the molten slag from the annular pocket surrounding said gas outlet, means for quenching the molten slag, and means for recycling at least some of said quenched slag to said combustion chamber.

References Cited in the le of this patent UNITED STATES PATENTS 1,427,176 Taylor Aug. 29, 1922 1,680,183 Szilda et al. Aug. 7, 1928 FOREIGN PATENTS 1,025,395 France Apr. 14, 1953 9,307 Great Britain Apr. 22, 1907 

